The present invention relates to a display driving device for driving a display element such as a liquid crystal, a display device including the display element driving device, an information processing apparatus including the display device, and a display element driving method.
FIG. 21 shows a circuit of a conventional data driver disclosed in Japanese Unexamined Patent Publication No. 6-222741. In this data driver, by using voltages V1 to V9 having nine levels and externally driven, a 64-level applied voltages are applied to signal lines. The three upper bits of digital data of an image signal are converted into 8-value data by a decoder 923. Voltage selection circuits 927 and 925 select corresponding ones of the voltages V1 to V9 on the basis of the 8-value data, and output the selected voltages as VH and VL, respectively. The three lower bits of the digital data of the image signal are converted into 8-value data by a decoder 924. A resistor division scheme D/A converter 926 selects one of voltages obtained by equally dividing the voltages VH and VL by eight and outputs the selected voltage to a signal line as Vout. Even if the conventional arrangement is used, when the externally input voltages V1 to V9 are optimized in accordance with the xcex3 characteristics of a liquid-crystal element, xcex3-correction can be performed to some extent.
However, since an output voltage is generated by interpolating the voltages V1 to V9 in the above method, the resultant output voltage is different from a voltage to be displayed in an original state, and display characteristics are degraded disadvantageously.
On the other hand, FIG. 22 shows a case wherein xcex3-correction is performed by using a data driver using an analog scheme. In this method, an image signal is converted into analog data by a D/A converter 930. A xcex3-correction circuit 934 performs a xcex3-correction process on the basis of the analog data and correction data from a xcex3-correction table ROM 932. Therefore, analog data subjected to xcex3-correction is input to an analog-type data driver 942 in a liquid-crystal display device 940.
However, the analog-type data driver 942 has high power consumption because an analog circuit must be incorporated in the data driver 942, and the data driver 942 is generally improper for a display of a portable computer.
In recent years, it is tried to integrally form the data driver 942 or the like on a substrate having a TFT (thin-film transistor) 944. When the TFT 944 is integrally formed, a considerable reduction in size of the liquid-crystal display device and a reduction in cost can be realized. When such integral formation is to be performed, an incorporated analog circuit must be also constituted by a TFT in the analog-type data driver. 942. However, when the analog circuit is constituted by a TFT, the following various problems are posed. That is, the transistor characteristics of the TFT change with time, or it is difficult to obtain desired performance. In addition, when it is tried to incorporate the xcex3-correction circuit 934 in the data driver 942, a large amount of current flows in the xcex3-correction circuit 934 serving as an analog circuit. For this reason, a problem of a change in transistor characteristics of a TFT with time is posed.
As described above, the conventional data driver has various problems.
Some information processing apparatus such as a multi-media terminal or a graphic accelerator do not process an RGB signal used in a liquid-crystal display device, but process an image signal called a YUV or processes both RGB and YUV. When the liquid-crystal display device is used as a display of the information processing apparatus, it is desired that both the image signals, i.e., RGB and YUV, can be displayed. For this purpose, in a conventional arrangement, a conversion circuit 950 as shown in FIG. 23 is arranged to convert a YUV signal into an RGB signal, D/A conversion is performed by the D/A converter 952, and analog data obtained by the D/A conversion is applied to a data driver 962.
However, in this arrangement, since an analog-type data driver must be used as the data driver 962, a problem about an increase in power consumption is also posed as described above. In addition, there is a problem of difficulty of the data driver 962 integrally formed on a substrate on which a TFT 964 is formed.
The present invention has been made to solve the above problems, and has as its object to provide a display element driving device, a display device, an information processing apparatus, and a display element driving method each of which can obtain a low power consumption, can be increased in scale, and exhibit high performance.
It is another object of the present invention to provide a display element driving device or the like which can compensate for the display characteristics of a display element with an arrangement having low power consumption and a small scale.
It is still another object of the present invention to provide a display element driving device or the like which can display image signals having different formats with an arrangement having a low power consumption and a small scale.
It is still another object of the present invention to provide a display element driving device or the like which is optimally integrated with a substrate on which a TFT and the like are formed.
In order to solve the above problems, according to the present invention, there is provided a display element driving device comprising a D/A converter for giving an applied voltage based on a given image signal to an electrode line electrically connected to the other side of a capacitive display element having one side to which a given voltage is applied.
The D/A converter includes first to Nth charge storage means for respectively receiving first to Nth digital data corresponding to the image signal and storing charges corresponding to the values of the first to Nth digital data first to Nth connection means for electrically connecting the first to Nth charge storage means and the electrode line to each other and discharging the charges stored in the first to Nth charge storage means to the electrode line at a given timing.
According to the present invention, for example, in case of N=2, a charge corresponding to the value of the first digital data and a charge corresponding to the value of the second digital data are stored in the first charge storage means and the second charge storage means. When the first and second connection means electrically connects the first and second charge storage means and the electrode line to each other, the charges stored in the first and second charge storage means are discharged to the electrode line. At this time, on the basis of the discharged charges, capacitances of, e.g., the display element, the electrode line, and the first and second charge storage means, and the like, an applied voltage to the electrode line is determined. According to the present invention, the moment D/A conversion is performed, processes such as addition and subtraction processes between the digital data are performed or the process multiplying the digital data by given coefficients can be performed.
The present invention is characterized in that the first to Nth charge storage means store the charges on the basis of the first to Nth digital data can be performed and at least one given voltage. In this manner, when various-given voltages are prepared, or a given voltage is changed, not only a simple addition process of digital data but also various processes such as a subtraction process, a multiplication process of a coefficient can be easily performed.
The present invention is characterized in that the first to Nth charge storage means include capacitor elements having one sides to which a given voltage is applied and capacitances which are binarily weighted, and the first to Nth connection means include switches for electrically connecting the other sides of the capacitive elements and the electrode line to each other at once. When the capacitances of the capacitor elements are binarily weighted at, e.g., 1:2:4:8 . . . , an addition process, a subtraction process, and the like of digital data can be easily performed.
The present invention is characterized in that the first to Nth charge storage means select at least one capacitor element for storing a charge from the capacitor elements on the basis of the first to Nth digital data, and store a charge in the selected capacitor element at at least one given voltage. For example, given voltages V1, VC, and xe2x88x92V1 (V1xe2x88x92VC=VCxe2x88x92(xe2x88x92V1)), the first charge storage means selects a capacitor element for storing a charge by V1 and VC on the basis of the first digital data, and the second charge storage means selects a capacitor element for storing a charge by xe2x88x92V1 and VC, thereby making it possible to perform a subtraction process or the like. When the given voltages to the first to Nth charge storage means are made different from each other, a display element driving device which has a small scale and is not adversely affected by a variation in manufacturing process can be realized.
The present invention is characterized in that digital data having the complementary format of 2 is input as the first to Nth digital data, and the capacitance of the capacitor element corresponding to an MSB of digital data of capacitor elements included in at least one of the first to Nth charge storage means is made equal to the capacitance of a capacitor element corresponding to an LSB. For example, when digital data to be added is negative, a charge is stored in a capacitor corresponding to the MSB (Most Significant Bit), so that a subtraction process or the like of digital data having the complementary format of 2 can be realized.
According to the present invention, there is provided a display element driving device comprising a D/A converter for giving an applied voltage based on a given image signal to an electrode line electrically connected to the other side of a capacitive display element having one side to which a given voltage is applied, characterized in that the D/A converter includes first charge storage means for receiving image digital data corresponding to the image signal and storing a charge corresponding to the value of the image digital data, second charge storage means for receiving correction digital data for compensating for the display characteristics of the display element and storing a charge corresponding to the value of the correction digital data, first correction means for electrically connecting the first charge storage means and the electrode line to each other and discharging the charge stored in the first charge storage means to the electrode line at a given timing, and second connection means for electrically connecting the second charge storage means and the electrode line to each other and discharging the charge stored in the charge storage means to the electrode line at the same timing as the given timing.
According to the present invention, D/A conversion of image digital data, a xcex3-correction process of a liquid crystal, and the like, can be simultaneously performed. In addition, the correction process can be accurately performed, and reductions in power consumption and reduction in scale of the device can also be performed.
The present invention is characterized in that when a change value of the applied voltage obtained when the LSB of the image digital data changes is represented by V1, and a change value of the applied voltage obtained when the LSB of the correction digital data changes is represented by V2, a relationship V1 greater than 2xc3x97V2 is established. In this manner, a state wherein an applied voltage decreases with respect to an increase in image digital data is prevented, and normal gradation expression can be performed.
The present invention is characterized in that when the number of bits of the image digital data is represented by m, and the number of bits of the correction digital data is represented by n, a relationship mxe2x89xa7n is established. In this manner, the display element driving device can be reduced in area while making normal gradation expression possible.
According to the present invention, there is provided a display element driving device for giving applied voltages VR1, VG1, and VB1 generated on the basis of digital data DY1, DU1, and DV1 of a YUV signal to electrode lines for red, green, and blue to which display elements are respectively electrically connected, characterized by comprising a first D/A converter for respectively receiving the digital data DY1 and DV1 and generating an applied voltage VR1 to the electrode line for red by conversion according to a relational expression VR1=aDY1+bDV1, a second D/A converter for respectively receiving the digital data DY1, DU1, and DV1 and generating an applied voltage VG1 to the electrode line for green by conversion according to a relational expression VG1=cDY1+dDU1+eDV1, and a third D/A converter for respectively receiving the digital data DY1 and DU1 and generating an applied voltage VB1 to the electrode for blue by conversion according to a relational expression VB1=fDY1+gDU1.
According to the present invention, D/A conversion, a conversion process from YUV to RGB, and the like can be simultaneously performed. In this manner, a display element driving device which is optimum for an information processing apparatus or the like using a YUV signal can be provided. According to the present invention, various types of YUV signals such as YUV422 or YUV411 signals can be converted into RGB signals.
The present invention is characterized by comprising a fourth D/A converter for respectively receiving digital data DY2 for generating VR2, VG2, and VB2 given to second electrode lines for red, green, and blue adjacent to the electrode lines for red, green, and blue and the digital data DV1 and generating an applied voltage VR2 to the second electrode line for red by conversion according to a relational expression VR2=aDY2+bDV1, a fifth D/A converter for respectively receiving the digital data DY2, DU1, and DV1 and generating an applied voltage VG2 to the second electrode line for green by conversion according to the relational expression VG2=cDY2+dDU1+eDV1, and a sixth D/A converter for respectively receiving the digital data DY2 and DU1 and generating an applied voltage VB2 to the second electrode line for blue by conversion according to a relational expression VB2=fDY2+gDU1. In this manner, a display element driving device having an arrangement which is optimum for conversion of a YUV signal, especially, in a YUV422 scheme can be provided.
The present invention is characterized in that the respective coefficients a, b, c, d, e, f, and g are determined by at least one given voltage and the capacitance of a capacitor element which is incorporated in the D/A converter and in which a charge is stored by the given voltage. As described above, when the D/A converters incorporate the capacitor elements, the coefficients a to g are preferably determined by the capacitances (e.g., total capacitance or capacitance corresponding to the LSB of digital data) of the capacitor elements and the given voltages.
The present invention is characterized in that the capacitances of the capacitor elements for determining the respective coefficients a, b, c, d, e, f, and g are made equal to each other, and the voltages for determining the respective coefficients a, b, c, d, e, f, and g are made different from each other. For example, when capacitances Ca to Cg for determining the coefficients a to g are equally set to CEQ, and voltages Va to Vg for determining the coefficients a to g are made different from each other, the coefficients a to g can be set to values which are different from each other. When the coefficient ratio is not an integer, this method is preferable because the method which can make the capacitances Ca to Cg equal to each other is not easily adversely affected by variation in manufacturing process.
The present invention is characterized in that the voltages for determining the respective coefficients a, b, c, d, e, f, and g are made equal to each other, and the capacitances of the capacitor elements for determining the respective coefficients a, b, c, d, e, f, and g are made different from each other. For example, when the voltage Va to Vg for determining the coefficients a to g are equally set to VEQ, and the capacitances Ca to Cg for determining the coefficients a to g are made different from each other. The coefficients a to g can be set to values which are made different from each other.
The present invention is characterized in that the display element is a capacitive display element having one side to which a given voltage is applied; the first D/A converter includes first and second charge storage means for respectively receiving DY1 and DV1 and storing charges according to the values of the DY1 and DV1 and first and second connection means for electrically connecting. The first and second charge storage means and the electrode line for red to each other and discharging the charges stored in the first and second charge storage means to the electrode line for red at a given timing; the second D/A converter includes third, fourth, and fifth charge storage means for respectively receiving DY1, DU1, and DV1 and storing charges according to the values of the DY1, DU1, and DV1 and third, fourth, and fifth connection means for electrically connecting the third, fourth, and fifth charge storage means. The electrode line for green to each other and discharging the charges stored in the third, fourth, and fifth charge storage means to the electrode line for green at a given timing; and the third D/A converter includes sixth and seventh charge storage means for respectively receiving DY1 and DU1 and storing charges according the values of the DY1 and DU1 and sixth and seventh connection means for electrically connecting the sixth and seventh charge storage means and the electrode line for blue to each other and discharging the charges stored in the sixth and seventh charge storage means to the electrode line for blue at a given timing. When the first to seventh charge storage means and the first to seventh connection means are arranged as described above, D/A conversion and conversion from YUV to RGB can be realized at a low power consumption with a relatively simple arrangement.
The present invention is characterized in that the display element is a capacitive display element having one side to which a given voltage is applied; the first D/A converter includes first and second charge storage means for respectively receiving DY1 and DV1 and storing charges according to the values of the DY1 and DV1 and first and second connection means for electrically connecting. The first and second charge storage means and the electrode line for red to each other and discharging the charges stored in the first and second charge storage means to the electrode line for red at a given timing; the second D/A converter includes third, fourth, and fifth charge storage means for respectively receiving DY1, DU1, and DV1 and storing charges according to the values of the DY1, DU1, and DV1 and third, fourth, and fifth connection means for electrically connecting. The third, fourth, and fifth charge storage means and the electrode line for green to each other and discharging the charges stored in the third, fourth, and fifth charge storage means to the electrode line for green at a given timing; the third D/A converter includes sixth and seventh charge storage means for respectively receiving DY1 and DU1 and storing charges according the values of the DY1 and DU1 and sixth and seventh connection means for electrically connecting. The sixth and seventh charge storage means and the electrode line for blue to each other and discharging the charges stored in the sixth and seventh charge storage means to the electrode line for blue at a given timing; the fourth D/A converter includes eighth and ninth charge storage means for respectively receiving DY2 and DV1 and storing charges according to the values of the DY2 and DV1 and eighth and ninth connection means for electrically connecting. The eighth and ninth charge storage means to the second electrode line for red to each other and discharging the charges stored in the eighth and ninth charge storage means to the second electrode line for red at a given timing; the fifth D/A converter includes tenth, eleventh, and twelfth charge storage means for respectively receiving DY2, DU1, and DV1 and storing charges according to the values of the DY2, DU1, and DV1 and tenth, eleventh, and twelfth connection means for electrically connecting the tenth, eleventh, and twelfth charge storage means. The second electrode line for green to each other and discharging the charges stored in the tenth, eleventh, and twelfth to the second electrode line for green at a given timing; and the sixth D/A converter includes thirteenth and fourteenth charge storage means for respectively receiving DY2 and DU1 and storing charges according to the values of the DY2 and DU1 and thirteenth and fourteenth connection means for electrically connecting the thirteenth and fourteenth charge storage means and the second electrode line for blue to each other and discharging the charges stored in the thirteenth and fourteenth charge storage means to the electrode line for blue at a given timing. When the first to fourteenth charge storage means and the first to fourteenth connection means are arranged as described above, D/A conversion and conversion from YUV to RGB can be realized at a low power consumption with a relatively simple arrangement.
The present invention is characterized in that digital data DR1, DG1, and DB1 of a RGB signal are further given, and a YUV mode for generating applied voltages VR1, VG1, and VB1 on the basis of the digital data DY1, DU1, and DV1 and an RGB mode for generating the applied voltages VR1, VG1, and VB1 on the basis of the digital data DR1, DG1, and DB1 are set.
According to the present invention, not only conversion from YUV to RGB but also D/A conversion of RGB digital data can also be performed. In this manner, a display element driving device which is optimum for an information processing apparatus or the like in which both YUV and RGB are set can be provided.
The present invention is characterized by comprising means for, in the RGB mode, inputting DR1 to the first D/A converter in place of DY1 and DV1, inputting DG1 to the second D/A converter in place of DY1, DU1 and DV1, and inputting DB1 to the third D/A converter in place of DY1 and DU1. In this manner, both the conversion processes in the RGB mode and the YUV mode can be realized by the first to third D/A converters, hardware resources can be effectively used.
The present invention is characterized in that digital data DR1, DG1, DB1, DR2, DG2, and DB2 of an RGB signal are further given, and a YUV mode for generating applied voltages VR1, VG1, VB1, VR2, VG2, and VB2 on the basis of the digital data DY1, DU1, DV1, and DY2 and an RGB mode for generating applied voltages VR1, VG1, VB1, VR2, VG2, and VB2 on the basis of the digital data DR1, DG1, DB1, DR2, DG2, and DB2 are arranged. In this manner, a display element driving device which is optimum for an information processing apparatus or the like in which both YUV422 and RGB are set can be provided.
The present invention is characterized by comprising means for, in the RGB mode, inputting DR1 to the first D/A converter in place of DY1 and DV1, inputting DG1 to the second D/A converter in place of DY1, DU1 and DV1, inputting DB1 to the third D/A converter in place of DY1 and DU1, inputting DR2 to the fourth D/A converter in place of DY2 and DV1, inputting DG2 to the fifth D/A converter in place of DY2, DU1, and DV1, and inputting DB2 to the sixth D/A converter in place of DY2 and DU1. In this manner, especially in conversion of a YUV signal in a YUV422 scheme, hardware resources can be effectively used.
According to the present invention, there is provided a display element driving device for giving first and second applied voltages for red, blue, and green generated on the basis of digital data of a YUV signal to first and second electrode lines for red, green, and blue to which display elements are respectively electrically connected, characterized by comprising a first transfer line for sequentially transferring digital data DY1, DY2, DY3, DY4 . . . DY2Kxe2x88x921 DY2k . . . DYL of the YUV signal, a second transfer line for sequentially transferring digital data DV1, DU1, DV2, DU2 . . . DVK, DUK . . . DVL/2, DUL/2 or DU1, DV1, DU2, DV2 . . . DUK, DVK . . . DUL/2, DVL/2 of the YUV signal, a first latch for latching DY2kxe2x88x921 of the first transfer line, a second latch for latching DVK or DUK of the second transfer line at a timing which is substantially the same as that of the first latch, a third latch for latching DUK or DVK of the second transfer line, a fourth latch for latching DY2K of the first transfer line at a timing which is substantially the same as that of the third latch, and first to sixth D/A converters for generating first and second applied voltages for red, green, and blue on the basis of DY2kxe2x88x921, DVK, DUK, and DY2K latched by the first to fourth latches.
According to the present invention, data can be caused to flow in the first and second transfer lines without any loss, and data transfer to the first to sixth D/A converters without any loss. For this reason, power consumption and scale of the device can be reduced.
The display device according to the present invention is characterized by comprising one of the display element driving device described above and a display element driven by the display element driving device. The display device according to the present invention further includes a substrate on which a switching element consisting of a thin-film transistor or a thin-film non-linear element is formed, characterized in that the display element driving device is integrally formed on the substrate. When the display element driving device is integrally formed on the substrate as described above, the display device can be reduced in outside dimension and cost.
According to the present invention, there is provided a display device comprising a display element driving device, a display element driven by the display element driving device, and a substrate on which a switching element consisting of a thin-film transistor or a thin-film non-linear element is formed, characterized in that the display element driving device includes a D/A converter for receiving image digital data and correction digital data for compensating for the display characteristics of the display element and outputting an applied voltage subjected to a correction process, and the display element driving device is integrally formed on the substrate.
According to the present invention, since the display element driving device can be integrally formed on the substrate of the TFT, the device can be reduced in scale and cost. The circuit in the display element driving device can be entirely constituted by a digital-based circuit, and the design for the display element driving device can be simplified.
The information processing apparatus according to the present invention is characterized by comprising any one of the display devices described above and at least one image signal output device for outputting an image signal given to the display device. The information processing apparatus according to the present invention comprises a display element driving device, a display device including a display element driven by the display element driving device, a first image signal output device for outputting digital data of a YUV signal, and a second image signal output device for outputting digital data of an RGB signal, and is characterized in that the display element driving device includes means for directly converting the digital data of the YUV signal into analog applied voltages for red, green, and blue to output the analog applied voltages when the digital data of the YUV signal is input, and converting the digital data of the RGB signal into analog applied voltages for red, green, and blue to output the analog applied voltages when the digital data of the RGB signal is input. In this manner, the display element driving device can be entirely constituted by a digital-based circuit, and an information processing apparatus in which both RGB and YUV are set can be reduced in power consumption and size.